1. Field of the Invention
The present invention relates to a road-ice detecting sensor intended for a runway, a road, etc., utilizing a fiber Bragg grating (FBG) which varies in the peak wavelength in light reflex according to strain, an installation method for the road-ice detecting sensor, and a road-ice detecting method.
2. Description of the Related Art
There are known road anti-icing systems in which optical-fiber road temperature sensors are arranged in the ground in the longitudinal direction of a road (for example, see Japanese Unexamined Patent Application Publication Nos. Hei 5-71111, Hei 10-104363, 2000-241563, and 2001-228263).
Temperature sensors using optical cables with FBGs are also known (for example, see Japanese Unexamined Patent Application Publication Nos. Hei 10-141922, 2001-42142, 2001-194249, 2003-254838, and 2003-344183).
The foregoing road antiicing systems, however, cannot directly sense the temperature of the road surface because they are arranged underground in the longitudinal direction of the road. Also, it is a problem that the systems have to be removed and reinstalled upon every periodic road repair.
As for the FBG-based temperature sensors, they also have a problem that they cannot measure accurate temperature if the FBGs are uncovered and subjected to external stress or dew condensation which changes the detection signals, and they cannot directly sense the temperature of the road surface. Another problem is that with the FBGs entirely fixed to a stationary member, uneven adhesion or variations in FBG expansion may occur, hindering stable temperature measurement.
Moreover, as for temperature sensors having their FBGs covered with tubular protective members, they measure the temperature of the air around the protective members because air temperature is transmitted from the protective members to the FBGs through the air inside the protective members. Consequently, if these temperature sensors are applied to a road antiicing system, what they measures the atmospheric temperature of the road, not the temperature of a subject road surface. It is problematic that they cannot directly sense the temperature of the road surface.